Colored enamel wires have been widely used in various electric facilities and are basically composed of metal wires and insulation coating layer(s) surrounding the wires. An enamel wire is conventionally prepared by the following procedures:
continuously drawing a metal wire to size.fwdarw.annealing the wire.fwdarw.cooling and drying the wire.fwdarw.coating the wire with one or more coating layers of flowable resin materials.fwdarw.curing the resin materials.fwdarw.hardening the resin materials (if necessary).
In addition to showing the functions of different wires to facilitate the winding operation of the wires and reduce man-made errors, the colored coating layers of enamel wires can provide enamel wires with an aesthetic appearance and make them more valuable.
The colors of conventional enamel wires are provided either by the synthetic resins in coating layers or by organic pigments/dyes. It is believed that inorganic (metal) pigments are not suitable for enamel wires because they will negatively affect the properties such as appearance and flexibility of enamel wires. When using organic pigments/dyes to provide enamel wires with different colors, a metal wire is coated with a coating comprising a polymer and an organic pigment/dye, dried and cured, and then the pigment/dye and/or the reaction product of the pigment/dye with the polymer can provide the wire with a desired color. However, a high temperature operation is generally adopted to bake the coating layer into a film. The baking temperature depends on the coatings and is generally above 300.degree. C. and up to 450.degree. C. Hence, the high temperature operation can cause the organic pigments/dyes to evaporate or decompose and resulting in property changes and a non-uniform color.
In view of the poor temperature resistance of organic pigments/dyes, the temperature resistance grade of conventional colored enamel wires is generally below F grade (i.e. less than 155.degree. C.). Wires coated with organic pigments/dyes-containing enamel also suffer from the disadvantages of narrow operation range, low productivity, non-uniform color, pinhole formation and catalyst (in furnace) poisoning. All the disadvantages will negatively affect the processing of enamel wires and their properties. Therefore, it is desirable to develop high temperature resistant colored enamel wires having colors not provided by the synthetic resins, being high temperature resistant, and being easily produced at low cost without changing the processing conditions.
The present invention can meet the above demands. Specifically, the present invention provides a enamel wire with desired color, high temperature resistance and long use span.